Lecture 2 (Features of the cerebrum; meninges & blood supply)

What are the parts of the parietal lobe?

- Post central Gyrus (Primary somatosensory cortex)

- Superior parietal lobule

- Inferior parietal lobule

What parts make up the inferior parietal lobule and where is it?

- Is located posteriorly to the postcentral gyrus and inferiorly to the intraparietal sulcus

- Made up of the Angular Gyrus and the supramarginal gyrus

What are the parts of the temporal lobe?

- Superior temporal gyrus (contains wernikles treatment)

- Middle temporal gyrus

- Inferior temporal gyrus

What makes up the auditory cortex?

1. Wernicke's Area = auditory association

2. Transverse temporal Gyri = Primary auditory cortex

Where is the insular cortex?

Is inside the lateral sulcus

What are parts of the occipital lobe?

- Calcarine sulcus: Comes off the parietal-occipital sulcus

- Primary visual cortex: Lesions here will cause blindness. Located either side of the calcarine sulcus

What is the corpus callosum?

- Is made of commisural fibres that run from one side of the cerebral hemisphere to the other side which connects most of the areas of the cerebral hemisphere with the other hemisphere

- The corpus callosum lies on the floor of the great longitudinal fissure

What artery runs along the superior surface of the corpus callosum?

Anterior cerebral artery

What is the corpus callosum made of?

- Made of large white matter (commissural) tract, connecting two cerebral hemispheres

- Has 4 regions the rostrum (beak), Genu (Bend), Body and splenium (thickest part)

What is the Fornix?

- Is responsible for consolidation of memory & recival of memory and storage of memory

- Is a small white matter tract (association)

- Connects the hippocampus and hypothalamus (Including mammillary bodies)

What is the septum pellucidum?

- Is a translucent thin membrane between the corpus callosum and fornix

- Forms midline divider for lateral ventricles

What is the limbic system concerned with?

- Emotion

- Behaviour

- Memory

- Smell

What is the limbic system composed of?

- Amygdala

- Hippocampus

- Parahippocampal gyrus

- Cingulate gyrus

- Fornix

- Hypothalamus

- Thalamus

What is the Diencephalon?

The area of the brain between the cerebral hemispheres and the brainstem

What are the 4 bilateral structures that make up the Diencephalon?

- Thalamus

- Hypothalamus

- Epithalamus

- Subthalamus (not easily seen)

What is the thalamus and its function?

- Composed of bilateral nuclei (Grey matter)

- "Relay station" for information entering and leaving the cerebral cortex

- Contain thalamocortical fibers (Connect the thalamus to the cortex) and Corticothalamic fibers (connect the cortex to the thalamus)

What is the hypothalamus and its function?

- Below/ventral to the thalamus

- Function is homeostatic regulation and Neuroendocrine functions (As neurons exert control by secreting hormones that affect the pituitary gland, which is the 'master gland' as it controls all the other endocrine glands in the body)

- The hypothalamus has two horns, one for the optic tract and the other attaches to the pituitary gland (the optic tract and chiasma bound to the hypothalamus)

Describe the Epithalamus?

- Posterior-dorsal diencephalic structure

- Consists of 1. Habenula and 2. Pineal gland

What is the Habenula?

Route between the limbic structures and the brainstem

What is the pineal gland?

Secretes melatonin which regulates the circadian rhythm (Secretes melatonin when it is dark and doesnt when it is light)

What is the ventricular system?

Is a network of interconnected "spaces" within the brain that are filled with cerebrospinal fluid, which nourishes and protects the brain

What produced cerebrospinal fluid?

Is produced by choroid plexus, which lines the ventricles

What is the basal ganglia?

- Are grey matter structures sitting deep in the base of the brain

- Is important for motor control

What are the parts of the basal ganglia?

- Caudate (head)

- Putamen

- Globus pallidus

- Caudate (tail)

What are the layers of the meninges?

- Dura Mater

- Arachnoid

- Pia Mater

What is the function of the meninges?

Protect the brain from trauma in two ways: Covering and cushioning

(does this by forming sinuses that allow blood-CSF circulation)

What are the two layers of dura mater?

1. Periosteal: Outermost, adjacent to bone of skull and lines the skull.

2. Meningeal layer: Innermost, which dips down/folds down into the major fissures which forms a dural folds.

What are the two dural specializations?

1. Dural reflection

2. Venous sinuses

What are dural reflections?

- Sheet-like protrusions from meningeal layer of dura mater into cranial cavity

- Separate major subdivisions of the brain

What are the three key dural reflections?

- Falx cerebri: Separates cerebral hemispheres, occupies longitudinal fissure (meingeal layer of dura-mater from both sides which connects to form a dural fold that is separating the two cerebral hemispheres)

- Falx cerebelli: Partially separates cerebellar hemispheres (Tiny dural fold)

- Tentorium cerebelli: Separates cerebrum from cerebellum, occupies transverse fissure.

Describe venous sinuses?

- Form between the two dural layers at edges of dural reflections (formed where dura matter dips down, veins inside the brain drain into these sinuses as well as CSF drain into these sinuses)

- Triangular in cross-section

- Drain cerebral veins and also reabsorb cerebrospinal fluid (CSF)

- Is not blood vessels

- Sagittal sinuses come together at confluence of the sinuses

- bilateral exit from the head via jugular veins

What is the Arachnoidmater?

- Adjacent to the innermost (meningeal) layer of the dura mater

- Small extensions called arachnoid trabeculae leave this layer and extend to pia

- Creates a space between (Between arachnoid and pia) called the subarachnoid space in which the cerebrospinal fluid (CSF) circulates (cerebral arteries and veins also travel in this area, adjacent to pia mater.

What are arachnoid villi?

- Structures that return CSF into the venous circulation into the sinuses

- Protrude into dural sinuses (esp. superior sagittal sinus)

What is the pia mater?

- Closely adherent to the brain, thin, transparent

- Closely invests all contours and folds of cerebral and cerebellar cortices (dips into all the sulci)

What is the difference the spinal cord meninges has compared to the brains?

- Dura mater of spinal has only a single layer = meningeal layer which associates with arachnoid

- Periosteal layer replaced by adipose (epidural space/epidural fat)

What is a lumbar cistern?

- large subarachnoid space beginning ~L2 and proceeding caudally till S2 (~spinal cord ends at L1 or L2)

- Lumbar puncture can occur here

How much CSF is there and how often is it produced?

- Approx 130mls of CSF (~20mls in ventricles)

- Rate of production = 0.2-0.7 mls/min (~independent of blood and ventricular pressure)

What is the flow path of CSF?

1. CSF is produced in the choroid plexuses (In lateral ventricle)

2. Through the intraventricular foramen

3. Subarachnoid plexus in the 3rd ventricle which also produces CSF

4. Travels through the cerebral aqueduct

5. Into the 4th Ventricle

6. Travels through apertures into the subarachnoid space

7. Travels into the sinuses

8. CSF into the blood into the internal jugular vein

What is a Hydrocephalus?

Hydrocephalus = Circulation of CSF is blocked, but CSF production continues

- Individual ventricles may be affected

- Shunt may be put in place to bypass obstruction

What are the arteries that bring blood to the brain?

Blood enters cerebral vasculature through two routes:

1. Rostral via internal carotid arteries

2. Caudal via basilar artery, fed from two paired vertebral arteries

What is the circle of Willis?

- Distributes arterial blood to various regions of the brain

- Helps prevent damage if one vessel becomes occluded (so if one area is blocked it can take over to some extent)

What are the four major routes of blood into the brain?

1. Anterior cerebral artery

2. Middle cerebral artery

3. Posterior cerebral artery

4. Vertebro basilar arteries

What does the anterior cerebral artery supply?

- Supplies the anterior 2/3 of medial aspect of cerebral hemispheres

- Corpus callosum; anterior portions of basal ganglia and internal capsule; olfactory bulb and tract

What does the middle cerebral artery supply?

- Supplies nearly all of the lateral surface of the cerebral hemispheres

- Deep perforating branches supply basal ganglia + internal capsule

What does the posterior cerebral artery supply?

- Supplies the posterior 1/3 of the medial aspect of the cerebral hemisphere

- Occipital lobe, inferior temporal lobe, superior brainstem

What arteries supply the cerebellum and brainstem?

ther vertebro-basilar arteries